1. Field of the Invention
The present invention relates generally to hydraulic or pneumatic fittings. More specifically, the field of the invention is that of brazed fittings for forming hydraulic couplings.
2. Description of the Related Art
Hydraulic fittings are conventionally of brazed construction, particularly those fittings having a specially shaped design. Conventional brazed fittings are manufactured by a press fit methodology, whereby the typically steel components are bored or counterbored to a precise diameter. There is usually a lead-in taper of 45.degree. at the outer end of the conduit which has counterbore aiding in locating the mating port. The conduit end includes a spigot which enters the counterbore with an interference fit of between 0.0005 inches and 0.005 inches, requiring that each part be made to a maximum tolerance of .+-.0.001125 inches. A brazing material, for example a pure copper or copper compound formed in a ring, is located between the bottom of the spigot and the base of the counterbore. During the heating, the brazing material melts and is drawn up the interference fit by capillary attraction. The brazing material diffuses and alloys with the metal of the components so that the interface between the spigot and the counterbore is stronger than material of the components. Ideally, the resulting integral fitting produces a high degree of integrity and reliably performs its intended function, while minimizing production costs.
An alternative to brazed fittings involves the use of multiple fittings which are required in order to connect different sized tubes, ports, etc.. However, the formation of the multiple connections requires additional material, as well as additional manufacturing time, which is duplicative and wasteful. Further, each connection provides another possible leak path for the pressurized medium within the fitting. Therefore, brazed fittings are preferable because they are generally less expensive to manufacture, less expensive to install, and have fewer potential leak paths.
However, on the rare occasions when a brazen fitting fails, the failure is typically catastrophic. For example, the intruding component of the brazed fitting may break loose from its mating part, usually while containing fluids under high pressure, resulting in a rapid deterioration of the hydraulic system. This is usually the result of the brazed fitting being poorly formed, typically due to insufficient "wetting" of the mating surfaces which are brazed together. The insufficient "wetting" may be due to misalignment or imprecise manufacture of the components which are press fit together. Additionally, poorly formed brazed fittings may leak in service, and also may contribute to improper alignment with other components in a system.
One particular problem with such fittings involves the intruding part being subject to misalignment during assembly. For example, the lead-in of the intruding conduit end may not be evenly aligned with the corresponding lead-in chamfer of the port which allows the conduit end to cant over prior to the application of assembly force. When assembly force is applied, the conduit end is driven down the chamfer and areas of alternating high and low interference fit are created. These areas of low integrity interference fit are areas of potential porosity and of weakness under pressurized loads.
Also, a common side effect of conventional brazing is the formation of a sharp-edged skin at the visible joint line between the assembled conduit end and the port. This is caused by the port gouging some material from the surface of the conduit end as it is press fit during assembly, and the gouged material is an unsightly blemish. Further, the seal between the brazed surfaces may become porous and have substantially reduced strength similar to misaligned components.
Another potential problem with conventional brazing techniques, although much rarer than the aforementioned problems, is that penetration of the brazing material into the interface between the mating surfaces may be insufficient to form a reliable brazed connection. The brazing connection depends on the mating surfaces being closely positioned, and on the brazing material being in contact with the mating surfaces when in the liquid state. If the mating surfaces are not properly formed, or the brazing material is not in contact with both of the mating surfaces, the liquid brazing material tends to flow away from the mating surfaces--being drawn by its own surface tension into a rounded mass of liquid away from the interface of the mating surfaces. After the rounded mass cools, it forms a solid mass which does not aid in bonding together the mating surfaces, and which also may go undetected until failure of the coupling.
What is needed is an improved method of brazing together components of hydraulic fittings.
A further need exists for a brazing method which aligns the components more precisely.
Another need exists for a brazing method which avoids gouging the components during manufacture.
Also needed is a brazing method which ensures penetration of the brazing material into the interface of mating surfaces.